Electrodeposition from copper electrolytes containing dithiocarbamate addition agents



United States Patent ELECTRODEPOSITION FROM COPPER ELECTRO- LYTES CONTAINING DITHIOCARBAMATE AD- DITION AGENTS Dennis R. Turner, New Providence, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application August 17, 1953, Serial No. 374,818

4 Claims. (Cl. 204-52 This invention relates to the electrodeposition of copper from electrolytes embodying certain addition agents to promote brighter and smootherplating.

' It is a general practice in the use of standard acid copper plating solutions and cyanide copper plating'solutions to add brightening agents thereto. For example, in acid copper plating solutions, a brightening agent comprising a mixture of thiourea or substituted thiourea compounds and dextrin is often used, whereas in cyanide cop per plating solutions, thiocyanates are sometimes used as a brightening agent. However, these known addition agents present problems that are well known in the plating art, such as control, purity of makeup, maintenance, and others. In many cases a mixture of two or more organic compounds are used as the addition agent and this further complicates the control of the plating bath.

An object of the present invention is to provide a brightening agent of a metal dialkyl dithio-carbamate suitable for use in both acid copper electrolytes and cyanide copper electrolytes.

A further object of the invention is to provide a process for electroplating copper from either an acid copper electrolyte or a cyanide copper electrolyte using a metal dialkyl dithiocarbamate as a brightening agent.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description.

I have discovered that the addition of selected amounts of one or more metal dialkyl dithiocarbamates to both acid copper electrolytes and cyanide copper electrolytes will enable electrodeposits having a highly refined grain size and smooth, bright surfaces, to be plated from the electrolyte so treated. Many of the disadvantages encountered with additions of previously known brightening agents to the same electrolytes are eliminated by the addition of the dithiocarbamate compounds. In particular, the dithiocarbamate compound can be used alone as a brightener, it is not necessary to add other types of organic addition agents, though I have found that other addition agents can be present in the electrolyte to advantage.

More particularly, the present invention is based on the addition of predetermined amounts of a metal dialkyl dithiocarbamate compound having the nucleus where M is a metal selected from the group consisting of cadmium, cobalt, nickel, and zinc, and R1, R2, R3, and R4 are the same or different alkyl analogs selected from at least one of the group consisting of monovalent hydrocarbon radicals containing from 1 to 6 carbon atoms. Various organic radicals may be substituted for any one of the R1, R2, R3, and R4 analogs so long as the resulting compound is not rendered so insoluble that it will not dissolve in the copper plating electrolyte inan amount 'pergallon of sulfuric acid (98%).

2,773,022 Patented Dec. 4, 1956 sutficient 'to produce an appreciable result. The addition compound may be initially dissolved in water or other liquid media before addition to the electrolyte, provided the solution produced is compatible with the electrolyte.

Examples of suitable addition compounds having the above nucleus are zinc dimethyl dithiocarbamate, zinc diethyl dithiocarbamate, zinc dibutyl dithiocarbamate, cadmium ethylmethyl dithiocarbamate, nickel dimethyl dithiocarbamate and cobalt 'diethyl dithiocarbamate, etc. I have found that as little as 0.0005 ounce per gallon of the dithiocarbamate addition agent will produce an improvement in copper plating electrolytes. The upper limit of the concentration is the point at which the electrolyte solution becomes saturated with the addition agent which is dependent upon the operatingtemperature of the plating bath. In acid copper plating, the operating temperature of the bath is generally around F. to F., thereby limiting the concentration of the dithiocarbamate addition agent to about 0.5 ounce per gallon. In cyanide copper plating electrolytes, the operating temperature is often around F whereby the concentration of the dithiocarbamate addition agent may be increased to about 1.0 ounce per gallon.

Acid copper electrolytes and cyanide copper electrolytes suitable for plating copper are well known. Any of these may be treated with the dialkyl metal dithiocarbamate addition agents of this invention with improved plating therefrom following. A suitable acid copper electrolyte is one comprising an aqueous solution having dissolved therein from 20 to 33 ounces per gallon of copper sulfate and from 1.3 to 13 ounces per gallon of sulfuric acid. In industry at the present time, the acid copper bathmost widely used is one comprising a solution of 27.5 ounces per gallon of copper sulfate crystals and 6 ounces A cyanide copper electrolyte finding general use is one comprising 7.5 to 9 ounces per gallon of copper (as metal), 0.8 to 1.5 ounces per gallon of free cyanide, and 4.0 to 6.0 ounces per gallon of either potassium hydroxide or sodium hydroxide. The cyanide copper bath most widely used is one comprising a solution of 8 ounces per gallon of copper (as metal), 1.0"ounce per gallon of free potassium cyanide,

and 4.0 ounces per gallon of potassium hydroxide.

The optimum proportions for the novel brightening agent. of this invention appears to be from 0.001 to 0.1 ounce per gallon of the metal dialkyl dithiocarbamate for both the acid copper electrolytes and the cyanide copper electrolytes, although beneficial results are obtained at lower and highenconcentrations-of. the addition agent. It will be appreciated that as the electrolyte is used in plating, the addition agent will require replenishing from time to time.

It is to be understood that the dithiocarbamate brightening agent of this invention may be used in combination with other addition agents in plating electrolytes. For example, excellent results have been obtained with dithiocarbamates in conjunction with thiohydantoins, and dextrin.

Acid copper electrolytes and cyanide copper electrolytes with the metal dialkyl dithiocarbamate as an addition agent may be employed for plating copper by passing either continuous direct current or periodically reversed electrical current or other suitable electrical current therethrough. Excellent results have been obtained with direct current plating from such electrolytes. However, periodically reversed current has given good electrodeposits characterized by the absence of nodules, and having smooth edges, smooth surfaces and refined grain not attainable with direct current.

The following examples are illustrative of the practice of the invention:

Example I An aqueous electroplating electrolyte of the following composition was prepared:

Ozs. per gal.

' Copper sulfate (crystals) [CLISO45H20] 27.5 Sulfuric acid (98%) 6 Zinc dirnethyl dit'niocarbamate .005

This bath was operated in a Hull Cell at 80 F. 7 Copper was plated on Hull Cell panels from the bath using 3 amperes total plating current. The copper plated panels produced were very bright over the entire surface.

Example II An aqueous electroplating electrolyte of the following composition was prepared:

025. per gal.

Copper (as metal) 8.0 Potassium cyanide 1.0 Potassium hydroxide 7.0 Zinc diethyl dithiocarbamate 0.8

This bath was operated in a Hull Cell at 170 F. Copper was plated on panels from the bath using 3 amperes total plating current. The copper plated panels produced were full-bright over the entire area.

Example III An aqueous electroplating electrolyte of the following composition was prepared:

Ozs. per gal. Copper sulfate (crystals) [CuSO-1.5H20l 27.5 Sulfuric acid (98%) 6 Zinc dimethyl dithiocarbamate 0.005 1-acetyl-2-thiohyd'antoin 0.005 Dextrose 0.0 20

This bath was operated in both a 100 gallon tank pilot plant and on a commercial scale in a 1000 gallon tank at a temperature of 90 F. Copper was plated on members from the bath using 9 A. S. F. at the cathode. The copper plated members produced were bright, smooth and fine grained.

It is intended that all matter contained in the above specification shall be interpreted as illustrative and not in a limiting sense. I

I claim as my invention:

1. An aqueous electroplating electrolyte for plating bright or semi-bright copper as the sole metal to be plated, the electrolyte comprising an aqueous solution of a copper salt having admixed therein from .0005 to 1.0 ounce per gallon of a brightening agent having the nucleus 4. Where M is a metal selected from the group consisting of cadmium, cobalt, nickel, and zinc and R1, R2, Ra, R4 are selected from at least one of the group consisting of monovalent hydrocarbon radicals containing from 1 to 6 carbon atoms.

2. An aqueous electrolyte for electrodepositing bright or semi-bright. copper comprising essentially copper sulfate, sulfuric acid and from 0.0005 to 0.5 ounce per gallon of a brightening agent having the nucleus s H N- o where M is a metal selected from the group consisting of cadmium, cobalt, nickel, and zinc and R1, R2, R3, and R4 are selected from at least one of the group consisting of monovalent hydrocarbon radicals containing from 1 to 6 carbon atoms.

3. An aqueous cyanide copper electroplating electrolyte comprising essentially copper as the sole metal to be plated therefrom, free cyanide, alkali and from .0005 to 1.0 ounce per gallon of a brightening agent having the nucleus where M is a metal selected from the group consisting of cadmium, cobalt, nickel, and zinc and R1, R2, R3, R4 are selected from at least one of the group consisting of monovalent hydrocarbon radicals containing from 1 to 6 carbon atoms.

4. In the process of plating copper alone on a base with a copper electroplating electrolyte comprising an aqueous solution of a copper salt, the steps comprising adding to the electrolyte from .0005 to 1.0 ounce per gallon of a brightening agent having the nucleus References Cited in the file of this patent UNITED STATES PATENTS Phillips et'al. Aug. 7, 1951 Chester Jan. 10, 1956 

1. AN AQUEOUS ELECTROPLATING ELECTROLYTE FOR PLATING BRIGHT OR SEMI-BRIGHT COPPER AS THE SOLE METAL TO BE PLATED, THE ELECTROLYTE COMPRISING AN AQUEOUS SOLUTION OF A COPPER SALT HAVING ADMIXED THEREIN FROM .0005 TO 1.0 OUNCE PER GALLON OF A BRIGHTENING AGENT HAVING THE NUCLEUS 